As the wireless communication technologies become matured in recent years, various wireless communication systems have been developed and widely applied in people's daily life to satisfy the users' need for communication. Among these wireless communication systems, the 3GPP LTE (3rd Generation Partnership Project Long Term Evolution) communication system has experienced the rapidest development.
In the 3GPP LTE communication system, UEs that are to transmit data therebetween usually have to take a base station and a core network as media and transmit data via resources allocated by the base station. Although a concept of allowing the UEs to transmit data by directly contending for wireless resources (i.e., device-to-device (D2D) communication) has been proposed in the art and the industry, the existing contention-for-scheduling mechanisms all have a lot of drawbacks.
The existing contention-for-scheduling mechanisms are mainly divided into the purely distributed type and the central assistance type. The purely distributed type is based on the CSMA-CA (Carrier Sense Multiple Access with Collision Avoidance) protocol or the ALOHA protocol, and allows distributed D2D UEs to obtain wireless resources necessary for data transmission. However, the contention-for-scheduling mechanisms of the purely distributed type generally only allow contending for wireless resources on the time axis, and leave much time idle, so the spectrum utilization efficiency is relatively limited.
Additionally, in the contention-for-scheduling mechanism of the central assistance type, the base station needs to obtain the neighborship between D2D UEs and wireless resources needed. In practice, there might be a lot of D2D UEs, so obtaining such information necessitates a large amount of data exchanges. In such a case, having the base station be responsible for the resource scheduling will cause an excessive burden on the base station. Therefore, the contention-for-scheduling mechanisms of the central assistance type are difficult to be implemented.
Accordingly, an urgent need exists in the art to provide a resource scheduling mechanism that allows D2D UEs to obtain wireless resources necessary for direct mode communication with adjacent D2D UES in a distributed way in consideration of the spectrum utilization efficiency.